Well, some of you are probably waiting to spot the Perseid Meteor showers, but they tend to come to late for me, so I have just been watching the Moon move across the sky as if it might just bump into Jupiter. But of course it just misses it as shown in this Sky Safari Pro screenshot and then moves further and further away.
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| Sky Safari Pro shows he Moon has been zipping along passing Jupiter (Source: Palmia Observatory) |
Yeah, being up late enough to try to see some Perseids is hard, since it is so tempting to goto sleep much earlier than the Perseids. Then you can wake up early and have a leisurely brunch with a martini and several other patio critters like Chac Mool, Wise Owl and some griffins guarding the water fountain and a chance to catch up a bit more of "Enlightenment Now, The Case for Reason, Science, Humanism and Progress." For the rest of you, you still have another day or two of expected meteor showers, especially if you are up at say 3:00 AM. Good luck and clear skies!
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| Enjoying a martini on the patio with Pinker, Chac M0ol, Wise Owl and Griffins (Source: Palmia Observatory) |
After breakfast there is still time to catch up on some of the latest journal articles before it's time to head up to the monthly OCA general meeting. The latest issue of Quanta Magazine had an interesting article describing the ongoing tension between two separate approaches being used to measure Hubble Constant. Now Hubble's Constant is not really constant and the measured value has always been changing ever since it was first proposed. Now the value the Planck team reports is 67.4 kilometers per second per megaparsec, while the SHoES team, using standard light candles for Type 1a supernova, reports a value of 74.0 kilometers per second per megaparsec. This difference might not sound like much but in this age of increasing precision in astronomical cosmology, the difference exceeds the systematic and random error assessments for each method. This "tension" between the two measurement might indicate some still unresolved error source or flaw or on the other hand some new physics not yet included in one or both of the methods. The article goes on to describe the meeting just conducted at the Kavli Institute in Santa Barbara and another separate measurement method was presented and it comes in at right in the middle at 73.3
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| Has the tension between measurements of Hubble Constant turned into a problem? (Source: P. Hardzeiej, Quanta Magazine) |
So, the astronomers in attendance were ready to say that what had once just be tension has now sort of moved into the "problem" area. What to do about this? Well, you can check out the Quanta article for more of the details and the relationship between all of the several teams trying to improve and justify their own measurement.
It turns out just by chance, this month's general OCA meeting included a presentation on the mysteries of exploding stars by Anthony Piro of the Carnegie Observatories. It didn't occur to me to ask him about the controversy, but his presentation illuminated some of the details of the supernova standard candle approach and how important it is to get a better handle on the standard light output from a Type 1a supernova.
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| Professor Piro, Carnegie Observatories, explains the mystery of exploding stars at OCA general meeting (Source: Palmia Observatory) |
He divided his presentation into two parts. The first part dealt with the Type 1a supernovas, which are caused by a binary star system, where the high density white dwarf member of the pair steals gas and material from the orbiting star and when the accreted mass exceeds the Chandraskhar limit, the white dwarf explodes as a supernova, which can end mostly as a neutron star. This process, while not completely understood, is well enough known that the maximum light curve output can be used as a standard candle with which the distance can be established. The other major type of supernova, the Type II, occurs when a giant star has burned up all of its hydrogen and starts burning heavier elements, but eventually runs out of that fuel too and the whole star just collapses under the force of gravity.
The Quanta article said that the supernova teams are not able to just collect more supernova data because their systematic errors cannot be corrected by getting more data of the same type. But, in the article written by Piro and collaborators, new data obtained in the Near Infrared (NIR) can be used to reduce the systematic errors. So, this new data being collected should be able to help resolve the tension or problem between the Hubble constant methods. I can't quite get a sense of how this new set of observations helps, but you can see in the figure from the paper below that the NIR spectra provides a better view of what might be going on. Thanks for that Professor Piro!
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| NIR observations of Type Ia supernovas might help resolve Hubble tension? (Source: E. Hsiao et al, arXiv:1810.08213v2) |
In the second half of his presentation, Professor Piro then discussed whether Type II supernovas would have an electromagnetic signature or if the star would just collapse into a black hole without much emitted radiation. The current thinking was that the supernova would really just be an "unnova" and the star would just disappear from view and go directly to a black hole. But Piro presents in the abstract and paper referenced below that it is entirely likely that the collapse to a black hole could be preceded by an optical transient over a 3-10 day period. So we can see there is still plenty of mystery in exploding stars. Check out the details in the referenced paper. Thank you Professor Piro for an interesting meeting!
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| Will Type II Supernovas collapse to black holes exhibit EM signatures? (A. Piro, arXiv:1304.1539v1) |
So, we talked of novas, now we should mention a great episode of NOVA, which is just on TV now, titled "Back to the Moon." After the first visit to the moon over 50 years ago, there is a new resurgence of going back to the moon. What has driven this renewed interest? It seems that there is increased interest in mining titanium and other metals and maybe even Helium III for power generation, but the discovery of water, as frozen ice on the moon, is probably one of the big drivers of increased interest. If you haven't seen this NOVA episode, be sure to check it out. It is great!
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| NOVA episode explains how finding water on the moon is key discovery (Source: NOVA, S46, E11) |
Of special interest to me, was when the NOVA program introduced one of the original papers written in 1961 that summarized how it might be possible that water as frozen ice could still be present on the moon. There have been many theories about the formation of the Moon and the early Earth and what happened during their formation and what happened to all the water during the various bombardment phases of our history and when the surfaces of moons and planets were re-melted due to impact of asteroids and comets.
The paper, written in 1961 by Kenneth Watson, et al, looked at the main escape mechanisms, like solar wind and photoionization of water and other volatiles, which would result in the water escaping from the weak gravitational field of the moon and just escaping into space. So, the moon, with no atmosphere and no magnetic field, should mostly be dry except for the fortunate fact that the orbit and inclination of the moon is such that there are craters at the lunar poles that never have direct sight of the sun. The stability of ice at those locations indicates that ice could still be there even after several billion years. The paper estimated the loss of ice to outer space to be about 4 grams per square centimeter per billion years. Hey, that escape loss is so low that ice could still be in those craters, since the moon is just around 4 billion years old. You can check out the abstract of that paper below. The paper also includes another factor that I had not considered and that is the condensation of any escaped water vapor molecules that bounce around and they too can get recaptured and condensed on the cold traps in the sun shaded craters. Check out the paper for the other details and models and calculations.
So even though it is possible that ice could still be stable there after all of years, is it really there? If it is there than future visitors to the Moon could extract water from the ice and use it for drinking and breaking it down for hydrogen and oxygen for rocket fuel and breathing. Pretty neat?! It turns out that several missions to the Moon, which flew over the lunar poles, have indeed found evidence for ice there. The first mission was the LACROSS mission that used an expended rocket booster stage to impact a crater and examination of the plume of material expelled from the surface showed it contained water. The second mission was the Lunar Reconnaissance Orbiter (LRO) which spotted the tell tale spectra of ice when it flew over some of the craters. Again pretty neat!
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| NOVA referenced this paper that identified how water ice could be hidden on the moon (Source: Watson et al, JGR, Vol 66, No. 9, 1961) |
Hey, I know a dog walking buddy whose background and experience, based on casual exchanges on our walks, matches up very well with the author of that paper. Could it be the same person? Well, yes, indeed, he is the very same person and it has always been fun to bump into him as we walk our dogs, or Astronomer Assistants, as we refer to them! That is pretty neat, Ken! Congratulations on a paper, written over 50 years ago, while a graduate student at Caltech, which has helped reignite a big interest in returning to the moon!
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| Geophysicist Kenneth Watson and Geophysicist Assistant, Macallan (Source: Palmia Observatory) |
Until next time,
Resident Astronomer George
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